libcxx/include/__cxx03/__memory/shared_ptr.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___MEMORY_SHARED_PTR_H
  11 #define _LIBCPP___MEMORY_SHARED_PTR_H
  12
  13 #include <__cxx03/__compare/compare_three_way.h>
  14 #include <__cxx03/__compare/ordering.h>
  15 #include <__cxx03/__config>
  16 #include <__cxx03/__exception/exception.h>
  17 #include <__cxx03/__functional/binary_function.h>
  18 #include <__cxx03/__functional/operations.h>
  19 #include <__cxx03/__functional/reference_wrapper.h>
  20 #include <__cxx03/__fwd/ostream.h>
  21 #include <__cxx03/__iterator/access.h>
  22 #include <__cxx03/__memory/addressof.h>
  23 #include <__cxx03/__memory/allocation_guard.h>
  24 #include <__cxx03/__memory/allocator.h>
  25 #include <__cxx03/__memory/allocator_destructor.h>
  26 #include <__cxx03/__memory/allocator_traits.h>
  27 #include <__cxx03/__memory/auto_ptr.h>
  28 #include <__cxx03/__memory/compressed_pair.h>
  29 #include <__cxx03/__memory/construct_at.h>
  30 #include <__cxx03/__memory/pointer_traits.h>
  31 #include <__cxx03/__memory/uninitialized_algorithms.h>
  32 #include <__cxx03/__memory/unique_ptr.h>
  33 #include <__cxx03/__type_traits/add_lvalue_reference.h>
  34 #include <__cxx03/__type_traits/conditional.h>
  35 #include <__cxx03/__type_traits/conjunction.h>
  36 #include <__cxx03/__type_traits/disjunction.h>
  37 #include <__cxx03/__type_traits/is_array.h>
  38 #include <__cxx03/__type_traits/is_bounded_array.h>
  39 #include <__cxx03/__type_traits/is_constructible.h>
  40 #include <__cxx03/__type_traits/is_convertible.h>
  41 #include <__cxx03/__type_traits/is_reference.h>
  42 #include <__cxx03/__type_traits/is_unbounded_array.h>
  43 #include <__cxx03/__type_traits/nat.h>
  44 #include <__cxx03/__type_traits/negation.h>
  45 #include <__cxx03/__type_traits/remove_extent.h>
  46 #include <__cxx03/__type_traits/remove_reference.h>
  47 #include <__cxx03/__utility/declval.h>
  48 #include <__cxx03/__utility/forward.h>
  49 #include <__cxx03/__utility/move.h>
  50 #include <__cxx03/__utility/swap.h>
  51 #include <__cxx03/__verbose_abort>
  52 #include <__cxx03/cstddef>
  53 #include <__cxx03/new>
  54 #include <__cxx03/typeinfo>
  55 #if !defined(_LIBCPP_HAS_NO_ATOMIC_HEADER)
  56 #  include <__cxx03/__atomic/memory_order.h>
  57 #endif
  58
  59 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  60 #  pragma GCC system_header
  61 #endif
  62
  63 _LIBCPP_PUSH_MACROS
  64 #include <__cxx03/__undef_macros>
  65
  66 _LIBCPP_BEGIN_NAMESPACE_STD
  67
  68 // NOTE: Relaxed and acq/rel atomics (for increment and decrement respectively)
  69 // should be sufficient for thread safety.
  70 // See https://llvm.org/PR22803
  71 #if defined(__clang__) && __has_builtin(__atomic_add_fetch) && defined(__ATOMIC_RELAXED) && defined(__ATOMIC_ACQ_REL)
  72 #  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT
  73 #elif defined(_LIBCPP_COMPILER_GCC)
  74 #  define _LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT
  75 #endif
  76
  77 template <class _ValueType>
  78 inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_relaxed_load(_ValueType const* __value) {
  79 #if !defined(_LIBCPP_HAS_NO_THREADS) && defined(__ATOMIC_RELAXED) &&                                                   \
  80     (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
  81   return __atomic_load_n(__value, __ATOMIC_RELAXED);
  82 #else
  83   return *__value;
  84 #endif
  85 }
  86
  87 template <class _ValueType>
  88 inline _LIBCPP_HIDE_FROM_ABI _ValueType __libcpp_acquire_load(_ValueType const* __value) {
  89 #if !defined(_LIBCPP_HAS_NO_THREADS) && defined(__ATOMIC_ACQUIRE) &&                                                   \
  90     (__has_builtin(__atomic_load_n) || defined(_LIBCPP_COMPILER_GCC))
  91   return __atomic_load_n(__value, __ATOMIC_ACQUIRE);
  92 #else
  93   return *__value;
  94 #endif
  95 }
  96
  97 template <class _Tp>
  98 inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_increment(_Tp& __t) _NOEXCEPT {
  99 #if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && !defined(_LIBCPP_HAS_NO_THREADS)
 100   return __atomic_add_fetch(&__t, 1, __ATOMIC_RELAXED);
 101 #else
 102   return __t += 1;
 103 #endif
 104 }
 105
 106 template <class _Tp>
 107 inline _LIBCPP_HIDE_FROM_ABI _Tp __libcpp_atomic_refcount_decrement(_Tp& __t) _NOEXCEPT {
 108 #if defined(_LIBCPP_HAS_BUILTIN_ATOMIC_SUPPORT) && !defined(_LIBCPP_HAS_NO_THREADS)
 109   return __atomic_add_fetch(&__t, -1, __ATOMIC_ACQ_REL);
 110 #else
 111   return __t -= 1;
 112 #endif
 113 }
 114
 115 class _LIBCPP_EXPORTED_FROM_ABI bad_weak_ptr : public std::exception {
 116 public:
 117   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr() _NOEXCEPT                               = default;
 118   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr(const bad_weak_ptr&) _NOEXCEPT            = default;
 119   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr& operator=(const bad_weak_ptr&) _NOEXCEPT = default;
 120   ~bad_weak_ptr() _NOEXCEPT override;
 121   const char* what() const _NOEXCEPT override;
 122 };
 123
 124 _LIBCPP_NORETURN inline _LIBCPP_HIDE_FROM_ABI void __throw_bad_weak_ptr() {
 125 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 126   throw bad_weak_ptr();
 127 #else
 128   _LIBCPP_VERBOSE_ABORT("bad_weak_ptr was thrown in -fno-exceptions mode");
 129 #endif
 130 }
 131
 132 template <class _Tp>
 133 class _LIBCPP_TEMPLATE_VIS weak_ptr;
 134
 135 class _LIBCPP_EXPORTED_FROM_ABI __shared_count {
 136   __shared_count(const __shared_count&);
 137   __shared_count& operator=(const __shared_count&);
 138
 139 protected:
 140   long __shared_owners_;
 141   virtual ~__shared_count();
 142
 143 private:
 144   virtual void __on_zero_shared() _NOEXCEPT = 0;
 145
 146 public:
 147   _LIBCPP_HIDE_FROM_ABI explicit __shared_count(long __refs = 0) _NOEXCEPT : __shared_owners_(__refs) {}
 148
 149 #if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
 150   void __add_shared() noexcept;
 151   bool __release_shared() noexcept;
 152 #else
 153   _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_owners_); }
 154   _LIBCPP_HIDE_FROM_ABI bool __release_shared() _NOEXCEPT {
 155     if (__libcpp_atomic_refcount_decrement(__shared_owners_) == -1) {
 156       __on_zero_shared();
 157       return true;
 158     }
 159     return false;
 160   }
 161 #endif
 162   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __libcpp_relaxed_load(&__shared_owners_) + 1; }
 163 };
 164
 165 class _LIBCPP_EXPORTED_FROM_ABI __shared_weak_count : private __shared_count {
 166   long __shared_weak_owners_;
 167
 168 public:
 169   _LIBCPP_HIDE_FROM_ABI explicit __shared_weak_count(long __refs = 0) _NOEXCEPT
 170       : __shared_count(__refs),
 171         __shared_weak_owners_(__refs) {}
 172
 173 protected:
 174   ~__shared_weak_count() override;
 175
 176 public:
 177 #if defined(_LIBCPP_SHARED_PTR_DEFINE_LEGACY_INLINE_FUNCTIONS)
 178   void __add_shared() noexcept;
 179   void __add_weak() noexcept;
 180   void __release_shared() noexcept;
 181 #else
 182   _LIBCPP_HIDE_FROM_ABI void __add_shared() _NOEXCEPT { __shared_count::__add_shared(); }
 183   _LIBCPP_HIDE_FROM_ABI void __add_weak() _NOEXCEPT { __libcpp_atomic_refcount_increment(__shared_weak_owners_); }
 184   _LIBCPP_HIDE_FROM_ABI void __release_shared() _NOEXCEPT {
 185     if (__shared_count::__release_shared())
 186       __release_weak();
 187   }
 188 #endif
 189   void __release_weak() _NOEXCEPT;
 190   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __shared_count::use_count(); }
 191   __shared_weak_count* lock() _NOEXCEPT;
 192
 193   virtual const void* __get_deleter(const type_info&) const _NOEXCEPT;
 194
 195 private:
 196   virtual void __on_zero_shared_weak() _NOEXCEPT = 0;
 197 };
 198
 199 template <class _Tp, class _Dp, class _Alloc>
 200 class __shared_ptr_pointer : public __shared_weak_count {
 201   __compressed_pair<__compressed_pair<_Tp, _Dp>, _Alloc> __data_;
 202
 203 public:
 204   _LIBCPP_HIDE_FROM_ABI __shared_ptr_pointer(_Tp __p, _Dp __d, _Alloc __a)
 205       : __data_(__compressed_pair<_Tp, _Dp>(__p, std::move(__d)), std::move(__a)) {}
 206
 207 #ifndef _LIBCPP_HAS_NO_RTTI
 208   _LIBCPP_HIDE_FROM_ABI_VIRTUAL const void* __get_deleter(const type_info&) const _NOEXCEPT override;
 209 #endif
 210
 211 private:
 212   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override;
 213   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override;
 214 };
 215
 216 #ifndef _LIBCPP_HAS_NO_RTTI
 217
 218 template <class _Tp, class _Dp, class _Alloc>
 219 const void* __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__get_deleter(const type_info& __t) const _NOEXCEPT {
 220   return __t == typeid(_Dp) ? std::addressof(__data_.first().second()) : nullptr;
 221 }
 222
 223 #endif // _LIBCPP_HAS_NO_RTTI
 224
 225 template <class _Tp, class _Dp, class _Alloc>
 226 void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared() _NOEXCEPT {
 227   __data_.first().second()(__data_.first().first());
 228   __data_.first().second().~_Dp();
 229 }
 230
 231 template <class _Tp, class _Dp, class _Alloc>
 232 void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared_weak() _NOEXCEPT {
 233   typedef typename __allocator_traits_rebind<_Alloc, __shared_ptr_pointer>::type _Al;
 234   typedef allocator_traits<_Al> _ATraits;
 235   typedef pointer_traits<typename _ATraits::pointer> _PTraits;
 236
 237   _Al __a(__data_.second());
 238   __data_.second().~_Alloc();
 239   __a.deallocate(_PTraits::pointer_to(*this), 1);
 240 }
 241
 242 // This tag is used to instantiate an allocator type. The various shared_ptr control blocks
 243 // detect that the allocator has been instantiated for this type and perform alternative
 244 // initialization/destruction based on that.
 245 struct __for_overwrite_tag {};
 246
 247 template <class _Tp, class _Alloc>
 248 struct __shared_ptr_emplace : __shared_weak_count {
 249   template <class... _Args,
 250             class _Allocator                                                                         = _Alloc,
 251             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 252   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&...) : __storage_(std::move(__a)) {
 253     static_assert(
 254         sizeof...(_Args) == 0, "No argument should be provided to the control block when using _for_overwrite");
 255     ::new ((void*)__get_elem()) _Tp;
 256   }
 257
 258   template <class... _Args,
 259             class _Allocator                                                                          = _Alloc,
 260             __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 261   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&... __args) : __storage_(std::move(__a)) {
 262     using _TpAlloc = typename __allocator_traits_rebind<_Alloc, __remove_cv_t<_Tp> >::type;
 263     _TpAlloc __tmp(*__get_alloc());
 264     allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), std::forward<_Args>(__args)...);
 265   }
 266
 267   _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT { return __storage_.__get_alloc(); }
 268
 269   _LIBCPP_HIDE_FROM_ABI _Tp* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }
 270
 271 private:
 272   template <class _Allocator                                                                         = _Alloc,
 273             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 274   _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
 275     __get_elem()->~_Tp();
 276   }
 277
 278   template <class _Allocator                                                                          = _Alloc,
 279             __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
 280   _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
 281     using _TpAlloc = typename __allocator_traits_rebind<_Allocator, __remove_cv_t<_Tp> >::type;
 282     _TpAlloc __tmp(*__get_alloc());
 283     allocator_traits<_TpAlloc>::destroy(__tmp, __get_elem());
 284   }
 285
 286   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override { __on_zero_shared_impl(); }
 287
 288   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
 289     using _ControlBlockAlloc   = typename __allocator_traits_rebind<_Alloc, __shared_ptr_emplace>::type;
 290     using _ControlBlockPointer = typename allocator_traits<_ControlBlockAlloc>::pointer;
 291     _ControlBlockAlloc __tmp(*__get_alloc());
 292     __storage_.~_Storage();
 293     allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, pointer_traits<_ControlBlockPointer>::pointer_to(*this), 1);
 294   }
 295
 296   // This class implements the control block for non-array shared pointers created
 297   // through `std::allocate_shared` and `std::make_shared`.
 298   //
 299   // In previous versions of the library, we used a compressed pair to store
 300   // both the _Alloc and the _Tp. This implies using EBO, which is incompatible
 301   // with Allocator construction for _Tp. To allow implementing P0674 in C++20,
 302   // we now use a properly aligned char buffer while making sure that we maintain
 303   // the same layout that we had when we used a compressed pair.
 304   using _CompressedPair = __compressed_pair<_Alloc, _Tp>;
 305   struct _ALIGNAS_TYPE(_CompressedPair) _Storage {
 306     char __blob_[sizeof(_CompressedPair)];
 307
 308     _LIBCPP_HIDE_FROM_ABI explicit _Storage(_Alloc&& __a) { ::new ((void*)__get_alloc()) _Alloc(std::move(__a)); }
 309     _LIBCPP_HIDE_FROM_ABI ~_Storage() { __get_alloc()->~_Alloc(); }
 310     _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT {
 311       _CompressedPair* __as_pair                = reinterpret_cast<_CompressedPair*>(__blob_);
 312       typename _CompressedPair::_Base1* __first = _CompressedPair::__get_first_base(__as_pair);
 313       _Alloc* __alloc                           = reinterpret_cast<_Alloc*>(__first);
 314       return __alloc;
 315     }
 316     _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _Tp* __get_elem() _NOEXCEPT {
 317       _CompressedPair* __as_pair                 = reinterpret_cast<_CompressedPair*>(__blob_);
 318       typename _CompressedPair::_Base2* __second = _CompressedPair::__get_second_base(__as_pair);
 319       _Tp* __elem                                = reinterpret_cast<_Tp*>(__second);
 320       return __elem;
 321     }
 322   };
 323
 324   static_assert(_LIBCPP_ALIGNOF(_Storage) == _LIBCPP_ALIGNOF(_CompressedPair), "");
 325   static_assert(sizeof(_Storage) == sizeof(_CompressedPair), "");
 326   _Storage __storage_;
 327 };
 328
 329 struct __shared_ptr_dummy_rebind_allocator_type;
 330 template <>
 331 class _LIBCPP_TEMPLATE_VIS allocator<__shared_ptr_dummy_rebind_allocator_type> {
 332 public:
 333   template <class _Other>
 334   struct rebind {
 335     typedef allocator<_Other> other;
 336   };
 337 };
 338
 339 template <class _Tp>
 340 class _LIBCPP_TEMPLATE_VIS enable_shared_from_this;
 341
 342 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.general-6
 343 // A pointer type Y* is said to be compatible with a pointer type T*
 344 // when either Y* is convertible to T* or Y is U[N] and T is cv U[].
 345 #if _LIBCPP_STD_VER >= 17
 346 template <class _Yp, class _Tp>
 347 struct __bounded_convertible_to_unbounded : false_type {};
 348
 349 template <class _Up, std::size_t _Np, class _Tp>
 350 struct __bounded_convertible_to_unbounded<_Up[_Np], _Tp> : is_same<__remove_cv_t<_Tp>, _Up[]> {};
 351
 352 template <class _Yp, class _Tp>
 353 struct __compatible_with : _Or< is_convertible<_Yp*, _Tp*>, __bounded_convertible_to_unbounded<_Yp, _Tp> > {};
 354 #else
 355 template <class _Yp, class _Tp>
 356 struct __compatible_with : is_convertible<_Yp*, _Tp*> {};
 357 #endif // _LIBCPP_STD_VER >= 17
 358
 359 // Constructors that take raw pointers have a different set of "compatible" constraints
 360 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.const-9.1
 361 // - If T is an array type, then either T is U[N] and Y(*)[N] is convertible to T*,
 362 //   or T is U[] and Y(*)[] is convertible to T*.
 363 // - If T is not an array type, then Y* is convertible to T*.
 364 #if _LIBCPP_STD_VER >= 17
 365 template <class _Yp, class _Tp, class = void>
 366 struct __raw_pointer_compatible_with : _And< _Not<is_array<_Tp>>, is_convertible<_Yp*, _Tp*> > {};
 367
 368 template <class _Yp, class _Up, std::size_t _Np>
 369 struct __raw_pointer_compatible_with<_Yp, _Up[_Np], __enable_if_t< is_convertible<_Yp (*)[_Np], _Up (*)[_Np]>::value> >
 370     : true_type {};
 371
 372 template <class _Yp, class _Up>
 373 struct __raw_pointer_compatible_with<_Yp, _Up[], __enable_if_t< is_convertible<_Yp (*)[], _Up (*)[]>::value> >
 374     : true_type {};
 375
 376 #else
 377 template <class _Yp, class _Tp>
 378 struct __raw_pointer_compatible_with : is_convertible<_Yp*, _Tp*> {};
 379 #endif // _LIBCPP_STD_VER >= 17
 380
 381 template <class _Ptr, class = void>
 382 struct __is_deletable : false_type {};
 383 template <class _Ptr>
 384 struct __is_deletable<_Ptr, decltype(delete std::declval<_Ptr>())> : true_type {};
 385
 386 template <class _Ptr, class = void>
 387 struct __is_array_deletable : false_type {};
 388 template <class _Ptr>
 389 struct __is_array_deletable<_Ptr, decltype(delete[] std::declval<_Ptr>())> : true_type {};
 390
 391 template <class _Dp, class _Pt, class = decltype(std::declval<_Dp>()(std::declval<_Pt>()))>
 392 true_type __well_formed_deleter_test(int);
 393
 394 template <class, class>
 395 false_type __well_formed_deleter_test(...);
 396
 397 template <class _Dp, class _Pt>
 398 struct __well_formed_deleter : decltype(std::__well_formed_deleter_test<_Dp, _Pt>(0)) {};
 399
 400 template <class _Dp, class _Yp, class _Tp>
 401 struct __shared_ptr_deleter_ctor_reqs {
 402   static const bool value = __raw_pointer_compatible_with<_Yp, _Tp>::value && is_move_constructible<_Dp>::value &&
 403                             __well_formed_deleter<_Dp, _Yp*>::value;
 404 };
 405
 406 template <class _Dp>
 407 using __shared_ptr_nullptr_deleter_ctor_reqs = _And<is_move_constructible<_Dp>, __well_formed_deleter<_Dp, nullptr_t> >;
 408
 409 #if defined(_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI)
 410 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI __attribute__((__trivial_abi__))
 411 #else
 412 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI
 413 #endif
 414
 415 template <class _Tp>
 416 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS shared_ptr {
 417   struct __nullptr_sfinae_tag {};
 418
 419 public:
 420 #if _LIBCPP_STD_VER >= 17
 421   typedef weak_ptr<_Tp> weak_type;
 422   typedef remove_extent_t<_Tp> element_type;
 423 #else
 424   typedef _Tp element_type;
 425 #endif
 426
 427   // A shared_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
 428   // any bookkeeping, so it's always trivially relocatable.
 429   using __trivially_relocatable = shared_ptr;
 430
 431 private:
 432   element_type* __ptr_;
 433   __shared_weak_count* __cntrl_;
 434
 435 public:
 436   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
 437
 438   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr(nullptr_t) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
 439
 440   template <class _Yp,
 441             __enable_if_t< _And< __raw_pointer_compatible_with<_Yp, _Tp>
 442   // In C++03 we get errors when trying to do SFINAE with the
 443   // delete operator, so we always pretend that it's deletable.
 444   // The same happens on GCC.
 445 #if !defined(_LIBCPP_CXX03_LANG) && !defined(_LIBCPP_COMPILER_GCC)
 446                                  ,
 447                                  _If<is_array<_Tp>::value, __is_array_deletable<_Yp*>, __is_deletable<_Yp*> >
 448 #endif
 449                                  >::value,
 450                            int> = 0>
 451   _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(_Yp* __p) : __ptr_(__p) {
 452     unique_ptr<_Yp> __hold(__p);
 453     typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 454     typedef __shared_ptr_pointer<_Yp*, __shared_ptr_default_delete<_Tp, _Yp>, _AllocT> _CntrlBlk;
 455     __cntrl_ = new _CntrlBlk(__p, __shared_ptr_default_delete<_Tp, _Yp>(), _AllocT());
 456     __hold.release();
 457     __enable_weak_this(__p, __p);
 458   }
 459
 460   template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
 461   _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d) : __ptr_(__p) {
 462 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 463     try {
 464 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 465       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 466       typedef __shared_ptr_pointer<_Yp*, _Dp, _AllocT> _CntrlBlk;
 467 #ifndef _LIBCPP_CXX03_LANG
 468       __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
 469 #else
 470     __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
 471 #endif // not _LIBCPP_CXX03_LANG
 472       __enable_weak_this(__p, __p);
 473 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 474     } catch (...) {
 475       __d(__p);
 476       throw;
 477     }
 478 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 479   }
 480
 481   template <class _Yp,
 482             class _Dp,
 483             class _Alloc,
 484             __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
 485   _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d, _Alloc __a) : __ptr_(__p) {
 486 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 487     try {
 488 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 489       typedef __shared_ptr_pointer<_Yp*, _Dp, _Alloc> _CntrlBlk;
 490       typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
 491       typedef __allocator_destructor<_A2> _D2;
 492       _A2 __a2(__a);
 493       unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
 494       ::new ((void*)std::addressof(*__hold2.get()))
 495 #ifndef _LIBCPP_CXX03_LANG
 496           _CntrlBlk(__p, std::move(__d), __a);
 497 #else
 498         _CntrlBlk(__p, __d, __a);
 499 #endif // not _LIBCPP_CXX03_LANG
 500       __cntrl_ = std::addressof(*__hold2.release());
 501       __enable_weak_this(__p, __p);
 502 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 503     } catch (...) {
 504       __d(__p);
 505       throw;
 506     }
 507 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 508   }
 509
 510   template <class _Dp>
 511   _LIBCPP_HIDE_FROM_ABI shared_ptr(
 512       nullptr_t __p,
 513       _Dp __d,
 514       __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs<_Dp>::value, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
 515       : __ptr_(nullptr) {
 516 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 517     try {
 518 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 519       typedef typename __shared_ptr_default_allocator<_Tp>::type _AllocT;
 520       typedef __shared_ptr_pointer<nullptr_t, _Dp, _AllocT> _CntrlBlk;
 521 #ifndef _LIBCPP_CXX03_LANG
 522       __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
 523 #else
 524     __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
 525 #endif // not _LIBCPP_CXX03_LANG
 526 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 527     } catch (...) {
 528       __d(__p);
 529       throw;
 530     }
 531 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 532   }
 533
 534   template <class _Dp, class _Alloc>
 535   _LIBCPP_HIDE_FROM_ABI shared_ptr(
 536       nullptr_t __p,
 537       _Dp __d,
 538       _Alloc __a,
 539       __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs<_Dp>::value, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
 540       : __ptr_(nullptr) {
 541 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 542     try {
 543 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 544       typedef __shared_ptr_pointer<nullptr_t, _Dp, _Alloc> _CntrlBlk;
 545       typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
 546       typedef __allocator_destructor<_A2> _D2;
 547       _A2 __a2(__a);
 548       unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
 549       ::new ((void*)std::addressof(*__hold2.get()))
 550 #ifndef _LIBCPP_CXX03_LANG
 551           _CntrlBlk(__p, std::move(__d), __a);
 552 #else
 553         _CntrlBlk(__p, __d, __a);
 554 #endif // not _LIBCPP_CXX03_LANG
 555       __cntrl_ = std::addressof(*__hold2.release());
 556 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 557     } catch (...) {
 558       __d(__p);
 559       throw;
 560     }
 561 #endif // _LIBCPP_HAS_NO_EXCEPTIONS
 562   }
 563
 564   template <class _Yp>
 565   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) _NOEXCEPT
 566       : __ptr_(__p),
 567         __cntrl_(__r.__cntrl_) {
 568     if (__cntrl_)
 569       __cntrl_->__add_shared();
 570   }
 571
 572 // LWG-2996
 573 // We don't backport because it is an evolutionary change.
 574 #if _LIBCPP_STD_VER >= 20
 575   template <class _Yp>
 576   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
 577       : __ptr_(__p), __cntrl_(__r.__cntrl_) {
 578     __r.__ptr_   = nullptr;
 579     __r.__cntrl_ = nullptr;
 580   }
 581 #endif
 582
 583   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
 584     if (__cntrl_)
 585       __cntrl_->__add_shared();
 586   }
 587
 588   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 589   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
 590     if (__cntrl_)
 591       __cntrl_->__add_shared();
 592   }
 593
 594   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
 595     __r.__ptr_   = nullptr;
 596     __r.__cntrl_ = nullptr;
 597   }
 598
 599   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 600   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
 601     __r.__ptr_   = nullptr;
 602     __r.__cntrl_ = nullptr;
 603   }
 604
 605   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 606   _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(const weak_ptr<_Yp>& __r)
 607       : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_ ? __r.__cntrl_->lock() : __r.__cntrl_) {
 608     if (__cntrl_ == nullptr)
 609       __throw_bad_weak_ptr();
 610   }
 611
 612 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
 613   template <class _Yp, __enable_if_t<is_convertible<_Yp*, element_type*>::value, int> = 0>
 614   _LIBCPP_HIDE_FROM_ABI shared_ptr(auto_ptr<_Yp>&& __r) : __ptr_(__r.get()) {
 615     typedef __shared_ptr_pointer<_Yp*, default_delete<_Yp>, allocator<__remove_cv_t<_Yp> > > _CntrlBlk;
 616     __cntrl_ = new _CntrlBlk(__r.get(), default_delete<_Yp>(), allocator<__remove_cv_t<_Yp> >());
 617     __enable_weak_this(__r.get(), __r.get());
 618     __r.release();
 619   }
 620 #endif
 621
 622   template <class _Yp,
 623             class _Dp,
 624             __enable_if_t<!is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
 625                               is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
 626                           int> = 0>
 627   _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
 628 #if _LIBCPP_STD_VER >= 14
 629     if (__ptr_ == nullptr)
 630       __cntrl_ = nullptr;
 631     else
 632 #endif
 633     {
 634       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 635       typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer, _Dp, _AllocT> _CntrlBlk;
 636       __cntrl_ = new _CntrlBlk(__r.get(), std::move(__r.get_deleter()), _AllocT());
 637       __enable_weak_this(__r.get(), __r.get());
 638     }
 639     __r.release();
 640   }
 641
 642   template <class _Yp,
 643             class _Dp,
 644             class              = void,
 645             __enable_if_t<is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
 646                               is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
 647                           int> = 0>
 648   _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
 649 #if _LIBCPP_STD_VER >= 14
 650     if (__ptr_ == nullptr)
 651       __cntrl_ = nullptr;
 652     else
 653 #endif
 654     {
 655       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
 656       typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer,
 657                                    reference_wrapper<__libcpp_remove_reference_t<_Dp> >,
 658                                    _AllocT>
 659           _CntrlBlk;
 660       __cntrl_ = new _CntrlBlk(__r.get(), std::ref(__r.get_deleter()), _AllocT());
 661       __enable_weak_this(__r.get(), __r.get());
 662     }
 663     __r.release();
 664   }
 665
 666   _LIBCPP_HIDE_FROM_ABI ~shared_ptr() {
 667     if (__cntrl_)
 668       __cntrl_->__release_shared();
 669   }
 670
 671   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr& __r) _NOEXCEPT {
 672     shared_ptr(__r).swap(*this);
 673     return *this;
 674   }
 675
 676   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 677   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr<_Yp>& __r) _NOEXCEPT {
 678     shared_ptr(__r).swap(*this);
 679     return *this;
 680   }
 681
 682   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr&& __r) _NOEXCEPT {
 683     shared_ptr(std::move(__r)).swap(*this);
 684     return *this;
 685   }
 686
 687   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
 688   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr<_Yp>&& __r) {
 689     shared_ptr(std::move(__r)).swap(*this);
 690     return *this;
 691   }
 692
 693 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
 694   template <class _Yp,
 695             __enable_if_t<!is_array<_Yp>::value && is_convertible<_Yp*, typename shared_ptr<_Tp>::element_type*>::value,
 696                           int> = 0>
 697   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(auto_ptr<_Yp>&& __r) {
 698     shared_ptr(std::move(__r)).swap(*this);
 699     return *this;
 700   }
 701 #endif
 702
 703   template <class _Yp,
 704             class _Dp,
 705             __enable_if_t<_And< __compatible_with<_Yp, _Tp>,
 706                                 is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*> >::value,
 707                           int> = 0>
 708   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(unique_ptr<_Yp, _Dp>&& __r) {
 709     shared_ptr(std::move(__r)).swap(*this);
 710     return *this;
 711   }
 712
 713   _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr& __r) _NOEXCEPT {
 714     std::swap(__ptr_, __r.__ptr_);
 715     std::swap(__cntrl_, __r.__cntrl_);
 716   }
 717
 718   _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT { shared_ptr().swap(*this); }
 719
 720   template <class _Yp, __enable_if_t<__raw_pointer_compatible_with<_Yp, _Tp>::value, int> = 0>
 721   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p) {
 722     shared_ptr(__p).swap(*this);
 723   }
 724
 725   template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
 726   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d) {
 727     shared_ptr(__p, __d).swap(*this);
 728   }
 729
 730   template <class _Yp,
 731             class _Dp,
 732             class _Alloc,
 733             __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
 734   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d, _Alloc __a) {
 735     shared_ptr(__p, __d, __a).swap(*this);
 736   }
 737
 738   _LIBCPP_HIDE_FROM_ABI element_type* get() const _NOEXCEPT { return __ptr_; }
 739
 740   _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator*() const _NOEXCEPT { return *__ptr_; }
 741
 742   _LIBCPP_HIDE_FROM_ABI element_type* operator->() const _NOEXCEPT {
 743     static_assert(!is_array<_Tp>::value, "std::shared_ptr<T>::operator-> is only valid when T is not an array type.");
 744     return __ptr_;
 745   }
 746
 747   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __cntrl_ ? __cntrl_->use_count() : 0; }
 748
 749 #if _LIBCPP_STD_VER < 20 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_SHARED_PTR_UNIQUE)
 750   _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI bool unique() const _NOEXCEPT { return use_count() == 1; }
 751 #endif
 752
 753   _LIBCPP_HIDE_FROM_ABI explicit operator bool() const _NOEXCEPT { return get() != nullptr; }
 754
 755   template <class _Up>
 756   _LIBCPP_HIDE_FROM_ABI bool owner_before(shared_ptr<_Up> const& __p) const _NOEXCEPT {
 757     return __cntrl_ < __p.__cntrl_;
 758   }
 759
 760   template <class _Up>
 761   _LIBCPP_HIDE_FROM_ABI bool owner_before(weak_ptr<_Up> const& __p) const _NOEXCEPT {
 762     return __cntrl_ < __p.__cntrl_;
 763   }
 764
 765   _LIBCPP_HIDE_FROM_ABI bool __owner_equivalent(const shared_ptr& __p) const { return __cntrl_ == __p.__cntrl_; }
 766
 767 #if _LIBCPP_STD_VER >= 17
 768   _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator[](ptrdiff_t __i) const {
 769     static_assert(is_array<_Tp>::value, "std::shared_ptr<T>::operator[] is only valid when T is an array type.");
 770     return __ptr_[__i];
 771   }
 772 #endif
 773
 774 #ifndef _LIBCPP_HAS_NO_RTTI
 775   template <class _Dp>
 776   _LIBCPP_HIDE_FROM_ABI _Dp* __get_deleter() const _NOEXCEPT {
 777     return static_cast<_Dp*>(__cntrl_ ? const_cast<void*>(__cntrl_->__get_deleter(typeid(_Dp))) : nullptr);
 778   }
 779 #endif // _LIBCPP_HAS_NO_RTTI
 780
 781   template <class _Yp, class _CntrlBlk>
 782   _LIBCPP_HIDE_FROM_ABI static shared_ptr<_Tp> __create_with_control_block(_Yp* __p, _CntrlBlk* __cntrl) _NOEXCEPT {
 783     shared_ptr<_Tp> __r;
 784     __r.__ptr_   = __p;
 785     __r.__cntrl_ = __cntrl;
 786     __r.__enable_weak_this(__r.__ptr_, __r.__ptr_);
 787     return __r;
 788   }
 789
 790 private:
 791   template <class _Yp, bool = is_function<_Yp>::value>
 792   struct __shared_ptr_default_allocator {
 793     typedef allocator<__remove_cv_t<_Yp> > type;
 794   };
 795
 796   template <class _Yp>
 797   struct __shared_ptr_default_allocator<_Yp, true> {
 798     typedef allocator<__shared_ptr_dummy_rebind_allocator_type> type;
 799   };
 800
 801   template <class _Yp,
 802             class _OrigPtr,
 803             __enable_if_t<is_convertible<_OrigPtr*, const enable_shared_from_this<_Yp>*>::value, int> = 0>
 804   _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(const enable_shared_from_this<_Yp>* __e, _OrigPtr* __ptr) _NOEXCEPT {
 805     typedef __remove_cv_t<_Yp> _RawYp;
 806     if (__e && __e->__weak_this_.expired()) {
 807       __e->__weak_this_ = shared_ptr<_RawYp>(*this, const_cast<_RawYp*>(static_cast<const _Yp*>(__ptr)));
 808     }
 809   }
 810
 811   _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(...) _NOEXCEPT {}
 812
 813   template <class, class _Yp>
 814   struct __shared_ptr_default_delete : default_delete<_Yp> {};
 815
 816   template <class _Yp, class _Un, size_t _Sz>
 817   struct __shared_ptr_default_delete<_Yp[_Sz], _Un> : default_delete<_Yp[]> {};
 818
 819   template <class _Yp, class _Un>
 820   struct __shared_ptr_default_delete<_Yp[], _Un> : default_delete<_Yp[]> {};
 821
 822   template <class _Up>
 823   friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
 824   template <class _Up>
 825   friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
 826 };
 827
 828 #if _LIBCPP_STD_VER >= 17
 829 template <class _Tp>
 830 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
 831 template <class _Tp, class _Dp>
 832 shared_ptr(unique_ptr<_Tp, _Dp>) -> shared_ptr<_Tp>;
 833 #endif
 834
 835 //
 836 // std::allocate_shared and std::make_shared
 837 //
 838 template <class _Tp, class _Alloc, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 839 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, _Args&&... __args) {
 840   using _ControlBlock          = __shared_ptr_emplace<_Tp, _Alloc>;
 841   using _ControlBlockAllocator = typename __allocator_traits_rebind<_Alloc, _ControlBlock>::type;
 842   __allocation_guard<_ControlBlockAllocator> __guard(__a, 1);
 843   ::new ((void*)std::addressof(*__guard.__get())) _ControlBlock(__a, std::forward<_Args>(__args)...);
 844   auto __control_block = __guard.__release_ptr();
 845   return shared_ptr<_Tp>::__create_with_control_block(
 846       (*__control_block).__get_elem(), std::addressof(*__control_block));
 847 }
 848
 849 template <class _Tp, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 850 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(_Args&&... __args) {
 851   return std::allocate_shared<_Tp>(allocator<__remove_cv_t<_Tp> >(), std::forward<_Args>(__args)...);
 852 }
 853
 854 #if _LIBCPP_STD_VER >= 20
 855
 856 template <class _Tp, class _Alloc, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 857 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
 858   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
 859   _ForOverwriteAllocator __alloc(__a);
 860   return std::allocate_shared<_Tp>(__alloc);
 861 }
 862
 863 template <class _Tp, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 864 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
 865   return std::allocate_shared_for_overwrite<_Tp>(allocator<__remove_cv_t<_Tp>>());
 866 }
 867
 868 #endif // _LIBCPP_STD_VER >= 20
 869
 870 #if _LIBCPP_STD_VER >= 17
 871
 872 template <size_t _Alignment>
 873 struct __sp_aligned_storage {
 874   alignas(_Alignment) char __storage[_Alignment];
 875 };
 876
 877 template <class _Tp, class _Alloc>
 878 struct __unbounded_array_control_block;
 879
 880 template <class _Tp, class _Alloc>
 881 struct __unbounded_array_control_block<_Tp[], _Alloc> : __shared_weak_count {
 882   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }
 883
 884   _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(
 885       _Alloc const& __alloc, size_t __count, _Tp const& __arg)
 886       : __alloc_(__alloc), __count_(__count) {
 887     std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::begin(__data_), __count_, __arg);
 888   }
 889
 890   _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(_Alloc const& __alloc, size_t __count)
 891       : __alloc_(__alloc), __count_(__count) {
 892 #  if _LIBCPP_STD_VER >= 20
 893     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
 894       // We are purposefully not using an allocator-aware default construction because the spec says so.
 895       // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
 896       std::uninitialized_default_construct_n(std::begin(__data_), __count_);
 897     } else {
 898       std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
 899     }
 900 #  else
 901     std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
 902 #  endif
 903   }
 904
 905   // Returns the number of bytes required to store a control block followed by the given number
 906   // of elements of _Tp, with the whole storage being aligned to a multiple of _Tp's alignment.
 907   _LIBCPP_HIDE_FROM_ABI static constexpr size_t __bytes_for(size_t __elements) {
 908     // When there's 0 elements, the control block alone is enough since it holds one element.
 909     // Otherwise, we allocate one fewer element than requested because the control block already
 910     // holds one. Also, we use the bitwise formula below to ensure that we allocate enough bytes
 911     // for the whole allocation to be a multiple of _Tp's alignment. That formula is taken from [1].
 912     //
 913     // [1]: https://en.wikipedia.org/wiki/Data_structure_alignment#Computing_padding
 914     size_t __bytes           = __elements == 0 ? sizeof(__unbounded_array_control_block)
 915                                                : (__elements - 1) * sizeof(_Tp) + sizeof(__unbounded_array_control_block);
 916     constexpr size_t __align = alignof(_Tp);
 917     return (__bytes + __align - 1) & ~(__align - 1);
 918   }
 919
 920   _LIBCPP_HIDE_FROM_ABI_VIRTUAL
 921   ~__unbounded_array_control_block() override {
 922   } // can't be `= default` because of the sometimes-non-trivial union member __data_
 923
 924 private:
 925   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
 926 #  if _LIBCPP_STD_VER >= 20
 927     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
 928       std::__reverse_destroy(__data_, __data_ + __count_);
 929     } else {
 930       __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
 931       std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
 932     }
 933 #  else
 934     __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
 935     std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
 936 #  endif
 937   }
 938
 939   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
 940     using _AlignedStorage = __sp_aligned_storage<alignof(__unbounded_array_control_block)>;
 941     using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
 942     using _PointerTraits  = pointer_traits<typename allocator_traits<_StorageAlloc>::pointer>;
 943
 944     _StorageAlloc __tmp(__alloc_);
 945     __alloc_.~_Alloc();
 946     size_t __size              = __unbounded_array_control_block::__bytes_for(__count_);
 947     _AlignedStorage* __storage = reinterpret_cast<_AlignedStorage*>(this);
 948     allocator_traits<_StorageAlloc>::deallocate(
 949         __tmp, _PointerTraits::pointer_to(*__storage), __size / sizeof(_AlignedStorage));
 950   }
 951
 952   _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
 953   size_t __count_;
 954   union {
 955     _Tp __data_[1];
 956   };
 957 };
 958
 959 template <class _Array, class _Alloc, class... _Arg>
 960 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Array>
 961 __allocate_shared_unbounded_array(const _Alloc& __a, size_t __n, _Arg&&... __arg) {
 962   static_assert(__libcpp_is_unbounded_array<_Array>::value);
 963   // We compute the number of bytes necessary to hold the control block and the
 964   // array elements. Then, we allocate an array of properly-aligned dummy structs
 965   // large enough to hold the control block and array. This allows shifting the
 966   // burden of aligning memory properly from us to the allocator.
 967   using _ControlBlock   = __unbounded_array_control_block<_Array, _Alloc>;
 968   using _AlignedStorage = __sp_aligned_storage<alignof(_ControlBlock)>;
 969   using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
 970   __allocation_guard<_StorageAlloc> __guard(__a, _ControlBlock::__bytes_for(__n) / sizeof(_AlignedStorage));
 971   _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
 972   std::__construct_at(__control_block, __a, __n, std::forward<_Arg>(__arg)...);
 973   __guard.__release_ptr();
 974   return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
 975 }
 976
 977 template <class _Tp, class _Alloc>
 978 struct __bounded_array_control_block;
 979
 980 template <class _Tp, size_t _Count, class _Alloc>
 981 struct __bounded_array_control_block<_Tp[_Count], _Alloc> : __shared_weak_count {
 982   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }
 983
 984   _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc, _Tp const& __arg)
 985       : __alloc_(__alloc) {
 986     std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count, __arg);
 987   }
 988
 989   _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc) : __alloc_(__alloc) {
 990 #  if _LIBCPP_STD_VER >= 20
 991     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
 992       // We are purposefully not using an allocator-aware default construction because the spec says so.
 993       // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
 994       std::uninitialized_default_construct_n(std::addressof(__data_[0]), _Count);
 995     } else {
 996       std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
 997     }
 998 #  else
 999     std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
1000 #  endif
1001   }
1002
1003   _LIBCPP_HIDE_FROM_ABI_VIRTUAL
1004   ~__bounded_array_control_block() override {
1005   } // can't be `= default` because of the sometimes-non-trivial union member __data_
1006
1007 private:
1008   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
1009 #  if _LIBCPP_STD_VER >= 20
1010     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
1011       std::__reverse_destroy(__data_, __data_ + _Count);
1012     } else {
1013       __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
1014       std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
1015     }
1016 #  else
1017     __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
1018     std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
1019 #  endif
1020   }
1021
1022   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
1023     using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, __bounded_array_control_block>;
1024     using _PointerTraits     = pointer_traits<typename allocator_traits<_ControlBlockAlloc>::pointer>;
1025
1026     _ControlBlockAlloc __tmp(__alloc_);
1027     __alloc_.~_Alloc();
1028     allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, _PointerTraits::pointer_to(*this), 1);
1029   }
1030
1031   _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
1032   union {
1033     _Tp __data_[_Count];
1034   };
1035 };
1036
1037 template <class _Array, class _Alloc, class... _Arg>
1038 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Array> __allocate_shared_bounded_array(const _Alloc& __a, _Arg&&... __arg) {
1039   static_assert(__libcpp_is_bounded_array<_Array>::value);
1040   using _ControlBlock      = __bounded_array_control_block<_Array, _Alloc>;
1041   using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, _ControlBlock>;
1042
1043   __allocation_guard<_ControlBlockAlloc> __guard(__a, 1);
1044   _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
1045   std::__construct_at(__control_block, __a, std::forward<_Arg>(__arg)...);
1046   __guard.__release_ptr();
1047   return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
1048 }
1049
1050 #endif // _LIBCPP_STD_VER >= 17
1051
1052 #if _LIBCPP_STD_VER >= 20
1053
1054 // bounded array variants
1055 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1056 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a) {
1057   return std::__allocate_shared_bounded_array<_Tp>(__a);
1058 }
1059
1060 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1061 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, const remove_extent_t<_Tp>& __u) {
1062   return std::__allocate_shared_bounded_array<_Tp>(__a, __u);
1063 }
1064
1065 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1066 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
1067   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
1068   _ForOverwriteAllocator __alloc(__a);
1069   return std::__allocate_shared_bounded_array<_Tp>(__alloc);
1070 }
1071
1072 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1073 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared() {
1074   return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>());
1075 }
1076
1077 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1078 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(const remove_extent_t<_Tp>& __u) {
1079   return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>(), __u);
1080 }
1081
1082 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
1083 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
1084   return std::__allocate_shared_bounded_array<_Tp>(allocator<__for_overwrite_tag>());
1085 }
1086
1087 // unbounded array variants
1088 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1089 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n) {
1090   return std::__allocate_shared_unbounded_array<_Tp>(__a, __n);
1091 }
1092
1093 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1094 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n, const remove_extent_t<_Tp>& __u) {
1095   return std::__allocate_shared_unbounded_array<_Tp>(__a, __n, __u);
1096 }
1097
1098 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1099 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a, size_t __n) {
1100   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
1101   _ForOverwriteAllocator __alloc(__a);
1102   return std::__allocate_shared_unbounded_array<_Tp>(__alloc, __n);
1103 }
1104
1105 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1106 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n) {
1107   return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n);
1108 }
1109
1110 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1111 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n, const remove_extent_t<_Tp>& __u) {
1112   return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n, __u);
1113 }
1114
1115 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
1116 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite(size_t __n) {
1117   return std::__allocate_shared_unbounded_array<_Tp>(allocator<__for_overwrite_tag>(), __n);
1118 }
1119
1120 #endif // _LIBCPP_STD_VER >= 20
1121
1122 template <class _Tp, class _Up>
1123 inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1124   return __x.get() == __y.get();
1125 }
1126
1127 #if _LIBCPP_STD_VER <= 17
1128
1129 template <class _Tp, class _Up>
1130 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1131   return !(__x == __y);
1132 }
1133
1134 template <class _Tp, class _Up>
1135 inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1136 #  if _LIBCPP_STD_VER <= 11
1137   typedef typename common_type<_Tp*, _Up*>::type _Vp;
1138   return less<_Vp>()(__x.get(), __y.get());
1139 #  else
1140   return less<>()(__x.get(), __y.get());
1141 #  endif
1142 }
1143
1144 template <class _Tp, class _Up>
1145 inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1146   return __y < __x;
1147 }
1148
1149 template <class _Tp, class _Up>
1150 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1151   return !(__y < __x);
1152 }
1153
1154 template <class _Tp, class _Up>
1155 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
1156   return !(__x < __y);
1157 }
1158
1159 #endif // _LIBCPP_STD_VER <= 17
1160
1161 #if _LIBCPP_STD_VER >= 20
1162 template <class _Tp, class _Up>
1163 _LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) noexcept {
1164   return compare_three_way()(__x.get(), __y.get());
1165 }
1166 #endif
1167
1168 template <class _Tp>
1169 inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1170   return !__x;
1171 }
1172
1173 #if _LIBCPP_STD_VER <= 17
1174
1175 template <class _Tp>
1176 inline _LIBCPP_HIDE_FROM_ABI bool operator==(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1177   return !__x;
1178 }
1179
1180 template <class _Tp>
1181 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1182   return static_cast<bool>(__x);
1183 }
1184
1185 template <class _Tp>
1186 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1187   return static_cast<bool>(__x);
1188 }
1189
1190 template <class _Tp>
1191 inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1192   return less<typename shared_ptr<_Tp>::element_type*>()(__x.get(), nullptr);
1193 }
1194
1195 template <class _Tp>
1196 inline _LIBCPP_HIDE_FROM_ABI bool operator<(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1197   return less<typename shared_ptr<_Tp>::element_type*>()(nullptr, __x.get());
1198 }
1199
1200 template <class _Tp>
1201 inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1202   return nullptr < __x;
1203 }
1204
1205 template <class _Tp>
1206 inline _LIBCPP_HIDE_FROM_ABI bool operator>(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1207   return __x < nullptr;
1208 }
1209
1210 template <class _Tp>
1211 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1212   return !(nullptr < __x);
1213 }
1214
1215 template <class _Tp>
1216 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1217   return !(__x < nullptr);
1218 }
1219
1220 template <class _Tp>
1221 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
1222   return !(__x < nullptr);
1223 }
1224
1225 template <class _Tp>
1226 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
1227   return !(nullptr < __x);
1228 }
1229
1230 #endif // _LIBCPP_STD_VER <= 17
1231
1232 #if _LIBCPP_STD_VER >= 20
1233 template <class _Tp>
1234 _LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, nullptr_t) noexcept {
1235   return compare_three_way()(__x.get(), static_cast<typename shared_ptr<_Tp>::element_type*>(nullptr));
1236 }
1237 #endif
1238
1239 template <class _Tp>
1240 inline _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr<_Tp>& __x, shared_ptr<_Tp>& __y) _NOEXCEPT {
1241   __x.swap(__y);
1242 }
1243
1244 template <class _Tp, class _Up>
1245 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1246   return shared_ptr<_Tp>(__r, static_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
1247 }
1248
1249 // LWG-2996
1250 // We don't backport because it is an evolutionary change.
1251 #if _LIBCPP_STD_VER >= 20
1252 template <class _Tp, class _Up>
1253 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1254   return shared_ptr<_Tp>(std::move(__r), static_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1255 }
1256 #endif
1257
1258 template <class _Tp, class _Up>
1259 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1260   typedef typename shared_ptr<_Tp>::element_type _ET;
1261   _ET* __p = dynamic_cast<_ET*>(__r.get());
1262   return __p ? shared_ptr<_Tp>(__r, __p) : shared_ptr<_Tp>();
1263 }
1264
1265 // LWG-2996
1266 // We don't backport because it is an evolutionary change.
1267 #if _LIBCPP_STD_VER >= 20
1268 template <class _Tp, class _Up>
1269 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1270   auto* __p = dynamic_cast<typename shared_ptr<_Tp>::element_type*>(__r.get());
1271   return __p ? shared_ptr<_Tp>(std::move(__r), __p) : shared_ptr<_Tp>();
1272 }
1273 #endif
1274
1275 template <class _Tp, class _Up>
1276 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1277   typedef typename shared_ptr<_Tp>::element_type _RTp;
1278   return shared_ptr<_Tp>(__r, const_cast<_RTp*>(__r.get()));
1279 }
1280
1281 // LWG-2996
1282 // We don't backport because it is an evolutionary change.
1283 #if _LIBCPP_STD_VER >= 20
1284 template <class _Tp, class _Up>
1285 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1286   return shared_ptr<_Tp>(std::move(__r), const_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1287 }
1288 #endif
1289
1290 template <class _Tp, class _Up>
1291 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
1292   return shared_ptr<_Tp>(__r, reinterpret_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
1293 }
1294
1295 // LWG-2996
1296 // We don't backport because it is an evolutionary change.
1297 #if _LIBCPP_STD_VER >= 20
1298 template <class _Tp, class _Up>
1299 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
1300   return shared_ptr<_Tp>(std::move(__r), reinterpret_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
1301 }
1302 #endif
1303
1304 #ifndef _LIBCPP_HAS_NO_RTTI
1305
1306 template <class _Dp, class _Tp>
1307 inline _LIBCPP_HIDE_FROM_ABI _Dp* get_deleter(const shared_ptr<_Tp>& __p) _NOEXCEPT {
1308   return __p.template __get_deleter<_Dp>();
1309 }
1310
1311 #endif // _LIBCPP_HAS_NO_RTTI
1312
1313 template <class _Tp>
1314 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS weak_ptr {
1315 public:
1316 #if _LIBCPP_STD_VER >= 17
1317   typedef remove_extent_t<_Tp> element_type;
1318 #else
1319   typedef _Tp element_type;
1320 #endif
1321
1322   // A weak_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
1323   // any bookkeeping, so it's always trivially relocatable.
1324   using __trivially_relocatable = weak_ptr;
1325
1326 private:
1327   element_type* __ptr_;
1328   __shared_weak_count* __cntrl_;
1329
1330 public:
1331   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR weak_ptr() _NOEXCEPT;
1332
1333   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1334   _LIBCPP_HIDE_FROM_ABI weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT;
1335
1336   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr const& __r) _NOEXCEPT;
1337
1338   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1339   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT;
1340
1341   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr&& __r) _NOEXCEPT;
1342
1343   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1344   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT;
1345
1346   _LIBCPP_HIDE_FROM_ABI ~weak_ptr();
1347
1348   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr const& __r) _NOEXCEPT;
1349   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1350   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT;
1351
1352   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr&& __r) _NOEXCEPT;
1353   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1354   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT;
1355
1356   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
1357   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT;
1358
1359   _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr& __r) _NOEXCEPT;
1360   _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT;
1361
1362   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __cntrl_ ? __cntrl_->use_count() : 0; }
1363   _LIBCPP_HIDE_FROM_ABI bool expired() const _NOEXCEPT { return __cntrl_ == nullptr || __cntrl_->use_count() == 0; }
1364   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> lock() const _NOEXCEPT;
1365   template <class _Up>
1366   _LIBCPP_HIDE_FROM_ABI bool owner_before(const shared_ptr<_Up>& __r) const _NOEXCEPT {
1367     return __cntrl_ < __r.__cntrl_;
1368   }
1369   template <class _Up>
1370   _LIBCPP_HIDE_FROM_ABI bool owner_before(const weak_ptr<_Up>& __r) const _NOEXCEPT {
1371     return __cntrl_ < __r.__cntrl_;
1372   }
1373
1374   template <class _Up>
1375   friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
1376   template <class _Up>
1377   friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
1378 };
1379
1380 #if _LIBCPP_STD_VER >= 17
1381 template <class _Tp>
1382 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
1383 #endif
1384
1385 template <class _Tp>
1386 inline _LIBCPP_CONSTEXPR weak_ptr<_Tp>::weak_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
1387
1388 template <class _Tp>
1389 inline weak_ptr<_Tp>::weak_ptr(weak_ptr const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
1390   if (__cntrl_)
1391     __cntrl_->__add_weak();
1392 }
1393
1394 template <class _Tp>
1395 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1396 inline weak_ptr<_Tp>::weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
1397   if (__cntrl_)
1398     __cntrl_->__add_weak();
1399 }
1400
1401 template <class _Tp>
1402 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1403 inline weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
1404   shared_ptr<_Yp> __s = __r.lock();
1405   *this               = weak_ptr<_Tp>(__s);
1406 }
1407
1408 template <class _Tp>
1409 inline weak_ptr<_Tp>::weak_ptr(weak_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
1410   __r.__ptr_   = nullptr;
1411   __r.__cntrl_ = nullptr;
1412 }
1413
1414 template <class _Tp>
1415 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1416 inline weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
1417   shared_ptr<_Yp> __s = __r.lock();
1418   *this               = weak_ptr<_Tp>(__s);
1419   __r.reset();
1420 }
1421
1422 template <class _Tp>
1423 weak_ptr<_Tp>::~weak_ptr() {
1424   if (__cntrl_)
1425     __cntrl_->__release_weak();
1426 }
1427
1428 template <class _Tp>
1429 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr const& __r) _NOEXCEPT {
1430   weak_ptr(__r).swap(*this);
1431   return *this;
1432 }
1433
1434 template <class _Tp>
1435 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1436 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT {
1437   weak_ptr(__r).swap(*this);
1438   return *this;
1439 }
1440
1441 template <class _Tp>
1442 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr&& __r) _NOEXCEPT {
1443   weak_ptr(std::move(__r)).swap(*this);
1444   return *this;
1445 }
1446
1447 template <class _Tp>
1448 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1449 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT {
1450   weak_ptr(std::move(__r)).swap(*this);
1451   return *this;
1452 }
1453
1454 template <class _Tp>
1455 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
1456 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT {
1457   weak_ptr(__r).swap(*this);
1458   return *this;
1459 }
1460
1461 template <class _Tp>
1462 inline void weak_ptr<_Tp>::swap(weak_ptr& __r) _NOEXCEPT {
1463   std::swap(__ptr_, __r.__ptr_);
1464   std::swap(__cntrl_, __r.__cntrl_);
1465 }
1466
1467 template <class _Tp>
1468 inline _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr<_Tp>& __x, weak_ptr<_Tp>& __y) _NOEXCEPT {
1469   __x.swap(__y);
1470 }
1471
1472 template <class _Tp>
1473 inline void weak_ptr<_Tp>::reset() _NOEXCEPT {
1474   weak_ptr().swap(*this);
1475 }
1476
1477 template <class _Tp>
1478 shared_ptr<_Tp> weak_ptr<_Tp>::lock() const _NOEXCEPT {
1479   shared_ptr<_Tp> __r;
1480   __r.__cntrl_ = __cntrl_ ? __cntrl_->lock() : __cntrl_;
1481   if (__r.__cntrl_)
1482     __r.__ptr_ = __ptr_;
1483   return __r;
1484 }
1485
1486 #if _LIBCPP_STD_VER >= 17
1487 template <class _Tp = void>
1488 struct owner_less;
1489 #else
1490 template <class _Tp>
1491 struct owner_less;
1492 #endif
1493
1494 template <class _Tp>
1495 struct _LIBCPP_TEMPLATE_VIS owner_less<shared_ptr<_Tp> > : __binary_function<shared_ptr<_Tp>, shared_ptr<_Tp>, bool> {
1496   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
1497     return __x.owner_before(__y);
1498   }
1499   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
1500     return __x.owner_before(__y);
1501   }
1502   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
1503     return __x.owner_before(__y);
1504   }
1505 };
1506
1507 template <class _Tp>
1508 struct _LIBCPP_TEMPLATE_VIS owner_less<weak_ptr<_Tp> > : __binary_function<weak_ptr<_Tp>, weak_ptr<_Tp>, bool> {
1509   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
1510     return __x.owner_before(__y);
1511   }
1512   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
1513     return __x.owner_before(__y);
1514   }
1515   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
1516     return __x.owner_before(__y);
1517   }
1518 };
1519
1520 #if _LIBCPP_STD_VER >= 17
1521 template <>
1522 struct _LIBCPP_TEMPLATE_VIS owner_less<void> {
1523   template <class _Tp, class _Up>
1524   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
1525     return __x.owner_before(__y);
1526   }
1527   template <class _Tp, class _Up>
1528   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
1529     return __x.owner_before(__y);
1530   }
1531   template <class _Tp, class _Up>
1532   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
1533     return __x.owner_before(__y);
1534   }
1535   template <class _Tp, class _Up>
1536   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
1537     return __x.owner_before(__y);
1538   }
1539   typedef void is_transparent;
1540 };
1541 #endif
1542
1543 template <class _Tp>
1544 class _LIBCPP_TEMPLATE_VIS enable_shared_from_this {
1545   mutable weak_ptr<_Tp> __weak_this_;
1546
1547 protected:
1548   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR enable_shared_from_this() _NOEXCEPT {}
1549   _LIBCPP_HIDE_FROM_ABI enable_shared_from_this(enable_shared_from_this const&) _NOEXCEPT {}
1550   _LIBCPP_HIDE_FROM_ABI enable_shared_from_this& operator=(enable_shared_from_this const&) _NOEXCEPT { return *this; }
1551   _LIBCPP_HIDE_FROM_ABI ~enable_shared_from_this() {}
1552
1553 public:
1554   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> shared_from_this() { return shared_ptr<_Tp>(__weak_this_); }
1555   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp const> shared_from_this() const { return shared_ptr<const _Tp>(__weak_this_); }
1556
1557 #if _LIBCPP_STD_VER >= 17
1558   _LIBCPP_HIDE_FROM_ABI weak_ptr<_Tp> weak_from_this() _NOEXCEPT { return __weak_this_; }
1559
1560   _LIBCPP_HIDE_FROM_ABI weak_ptr<const _Tp> weak_from_this() const _NOEXCEPT { return __weak_this_; }
1561 #endif // _LIBCPP_STD_VER >= 17
1562
1563   template <class _Up>
1564   friend class shared_ptr;
1565 };
1566
1567 template <class _Tp>
1568 struct _LIBCPP_TEMPLATE_VIS hash;
1569
1570 template <class _Tp>
1571 struct _LIBCPP_TEMPLATE_VIS hash<shared_ptr<_Tp> > {
1572 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_BINDER_TYPEDEFS)
1573   _LIBCPP_DEPRECATED_IN_CXX17 typedef shared_ptr<_Tp> argument_type;
1574   _LIBCPP_DEPRECATED_IN_CXX17 typedef size_t result_type;
1575 #endif
1576
1577   _LIBCPP_HIDE_FROM_ABI size_t operator()(const shared_ptr<_Tp>& __ptr) const _NOEXCEPT {
1578     return hash<typename shared_ptr<_Tp>::element_type*>()(__ptr.get());
1579   }
1580 };
1581
1582 template <class _CharT, class _Traits, class _Yp>
1583 inline _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
1584 operator<<(basic_ostream<_CharT, _Traits>& __os, shared_ptr<_Yp> const& __p);
1585
1586 #if !defined(_LIBCPP_HAS_NO_THREADS)
1587
1588 class _LIBCPP_EXPORTED_FROM_ABI __sp_mut {
1589   void* __lx_;
1590
1591 public:
1592   void lock() _NOEXCEPT;
1593   void unlock() _NOEXCEPT;
1594
1595 private:
1596   _LIBCPP_CONSTEXPR __sp_mut(void*) _NOEXCEPT;
1597   __sp_mut(const __sp_mut&);
1598   __sp_mut& operator=(const __sp_mut&);
1599
1600   friend _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
1601 };
1602
1603 _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
1604
1605 template <class _Tp>
1606 inline _LIBCPP_HIDE_FROM_ABI bool atomic_is_lock_free(const shared_ptr<_Tp>*) {
1607   return false;
1608 }
1609
1610 template <class _Tp>
1611 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load(const shared_ptr<_Tp>* __p) {
1612   __sp_mut& __m = std::__get_sp_mut(__p);
1613   __m.lock();
1614   shared_ptr<_Tp> __q = *__p;
1615   __m.unlock();
1616   return __q;
1617 }
1618
1619 template <class _Tp>
1620 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order) {
1621   return std::atomic_load(__p);
1622 }
1623
1624 template <class _Tp>
1625 _LIBCPP_HIDE_FROM_ABI void atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
1626   __sp_mut& __m = std::__get_sp_mut(__p);
1627   __m.lock();
1628   __p->swap(__r);
1629   __m.unlock();
1630 }
1631
1632 template <class _Tp>
1633 inline _LIBCPP_HIDE_FROM_ABI void atomic_store_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
1634   std::atomic_store(__p, __r);
1635 }
1636
1637 template <class _Tp>
1638 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
1639   __sp_mut& __m = std::__get_sp_mut(__p);
1640   __m.lock();
1641   __p->swap(__r);
1642   __m.unlock();
1643   return __r;
1644 }
1645
1646 template <class _Tp>
1647 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
1648 atomic_exchange_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
1649   return std::atomic_exchange(__p, __r);
1650 }
1651
1652 template <class _Tp>
1653 _LIBCPP_HIDE_FROM_ABI bool
1654 atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
1655   shared_ptr<_Tp> __temp;
1656   __sp_mut& __m = std::__get_sp_mut(__p);
1657   __m.lock();
1658   if (__p->__owner_equivalent(*__v)) {
1659     std::swap(__temp, *__p);
1660     *__p = __w;
1661     __m.unlock();
1662     return true;
1663   }
1664   std::swap(__temp, *__v);
1665   *__v = *__p;
1666   __m.unlock();
1667   return false;
1668 }
1669
1670 template <class _Tp>
1671 inline _LIBCPP_HIDE_FROM_ABI bool
1672 atomic_compare_exchange_weak(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
1673   return std::atomic_compare_exchange_strong(__p, __v, __w);
1674 }
1675
1676 template <class _Tp>
1677 inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_strong_explicit(
1678     shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
1679   return std::atomic_compare_exchange_strong(__p, __v, __w);
1680 }
1681
1682 template <class _Tp>
1683 inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_weak_explicit(
1684     shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
1685   return std::atomic_compare_exchange_weak(__p, __v, __w);
1686 }
1687
1688 #endif // !defined(_LIBCPP_HAS_NO_THREADS)
1689
1690 _LIBCPP_END_NAMESPACE_STD
1691
1692 _LIBCPP_POP_MACROS
1693
1694 #endif // _LIBCPP___MEMORY_SHARED_PTR_H